The present invention relates to a method and apparatus for obtaining a sample of liquid from near the bottom of a liquid-filled container and more particularly relates to a method and apparatus for obtaining a sample from a layer of water or water-oil emulsion underlying crude oil in a cargo tank.
In many instances, cargo oil, e.g. crude or refined oil which is loaded onto tanker ships is contaminated with substantial amounts of water. It can be easily understood that if payment for the purchased oils is based on the measured volume of total liquid in the cargo tanks, the final cost to a buyer may be substantially inflated since he pays for the useless water at cargo oil prices. In many actual cargo oil purchasing situations existing today, the buyer is allowed to deduct the volume of water in the cargo tanks only if he can prove that it was pumped aboard with the cargo oil and was not already present in the tanks before the cargo oil was loaded.
Since water inadvertently left in the tanks (e.g. seawater used for ballast, etc.), will have a substantially different composition from the water loaded with the cargo oil (e.g. formation water produced with the crude or condensate from steam used in processing the produced oil, etc.), the origin of the water in question can readily be established if a sample of the water can be obtained from a cargo tank for analysis after it has been loaded.
Further, by knowing the origin of any water in a loaded cargo tank, steps can be taken to alleviate the contamination problem. That is, if the water is being pumped in with the cargo oil, further processing of the cargo oil can be undertaken to remove the water before loading or if the water is originally present in the tank, further steps can be taken aboard the ship to remove such water before loading. Therefore, it can readily be seen that an important need exists for obtaining a sample of any water or water-oil emulsion that may be present in a cargo tank after it has otherwise been loaded with crude or refined oil.